Automotive air conditioning systems typically include a front mounted refrigerant condenser, an underhood refrigerant compressor, and an evaporator contained in an HVAC housing that is essentially inside the passenger compartment. The main inner volume of the compressor, the so called crankcase, is substantially hollow, but numerous moving components are either contained in it, or exposed to it, such as the central drive shaft (and support bearings), swash plate, and reciprocating pistons. During operation, refrigerant vapor running through the system (and the compressor) carries entrained oil, which reaches and lubricates the various moving part interfaces. When the compressor sits for extended periods of non operation, it is desirable that a substantial pool of lubricant remain at the bottom of the crankcase, to be available to lubricate the interfaces during start up.
Observation made prior to the subject invention found that, surprisingly, lubricant appeared to be actively leaving the compressor crankcase during periods of vehicle and compressor inactivity, and moving to the condenser, where it would not be immediately available at compressor start up. This appeared to be an incremental, rather than a precipitous process, but was still a concern, and the cause was not readily apparent. Detailed analysis found an explanation for this phenomenon, which was a pressure imbalance between the main crankcase volume of the compressor, and the suction cavity in the adjacent manifold. This imbalance was creating a condition by which liquid refrigerant and lubricant, which is miscible in the refrigerant, was subject to a combination of internal siphoning and pushing forces that pushed and pulled the liquid out of the compressor. Although the problem was better understood, a solution was not immediately apparent.